(1) Field of the Invention
The present invention relates generally to a remotely controlled vehicle designed for underwater operation, and in particular to a system for surveying the hydrography of a land area beneath a body of water, such as adjacent a shoreline.
(2) Description of the Prior Art
Determination of the hydrography, i.e., the underwater topography, of land beneath shallow bodies of water is often required for activities such as beach renourishment, in which the land altitude within up to about 1,500 feet of a beach must be determined both before and after renourishment activities. Similar measurements are required in other shallow water dredging activities.
Due to the turbulence of the water in these areas, simple measurement from a boat with a sounding device is not possible. When conventional surveying equipment is used, a surveyor's rod is carried out into the water by one individual, while another individual views the rod with a surveyor's level from the beach. This method is less than satisfactory, particularly where the water is more than four or five feet deep.
Other attempts have been made to address this need by towing a four-wheeled cart with an upwardly extending mast containing height markings across the area to be surveyed. The cart has been either carried out to the side of the area opposite the beach and pulled in to the beach with a cable or line, or the cart has been towed behind a boat or jet ski. This approach has also been less than satisfactory, since it is time consuming difficult for the surveyor to focus on the mast, and due to the fact that the turbulent water forces against the cable or line alters the path or the cart, and may cause the cart to capsize.
Thus, there is a continuing need for a method and apparatus for accurately measuring the hydrography of a land area beneath a shallow body of water, such as the water adjacent a beach.